Tire Pressure

#1
I'm trying to figure out the correct air pressure to run my 225/40 18's I've heard multiple different pressures any help and advice would be greatly appreciated.
 
#2
The recommended tire pressures should be listed in the owners manual of the car. You can also find them listed on the tire placard of the vehicle which you will usually find on the end of the drivers door, on the back side of the fuel door or on the underside of the trunk lid.
 
#4
What's an XL tire???

Unfortunately, really you need to see how they wear, but then it is too late.

Look at the max pressure on the sidewall. Some tires have 44-51 psi max pressure now, so you probably could run 35-40 psi easily.

Really though, if the center wears before the sides you need less pressure and if the sides wear out faster you need higher pressure.
 
#5
What's an XL tire???

Unfortunately, really you need to see how they wear, but then it is too late.

Look at the max pressure on the sidewall. Some tires have 44-51 psi max pressure now, so you probably could run 35-40 psi easily.

Really though, if the center wears before the sides you need less pressure and if the sides wear out faster you need higher pressure.
Extra load to make up for less sidewall I've tried to figure out if I need to run higher air pressure or not and if so how much.
 
#6
I don't think so.

Generally you will get better mileage and load carrying and harsher ride with higher tire pressure - but the key factor is how the tires will wear, and I can't tell you that.
 
#8
What's an XL tire???

Unfortunately, really you need to see how they wear, but then it is too late.

Look at the max pressure on the sidewall. Some tires have 44-51 psi max pressure now, so you probably could run 35-40 psi easily.

Really though, if the center wears before the sides you need less pressure and if the sides wear out faster you need higher pressure.
XL = Extra Load.

The air pressures listed on the sidewall of a tire at its maximum recommended pressures, not the recommended pressures.

Using tire pressures that high will make the tires ride like rocks, provide for poor handling and cause premature tire wear.

-- B.F.Goodrich T/A Certified Tire Specialist
 
#10
I'm trying to figure out the correct air pressure to run my 225/40 18's I've heard multiple different pressures any help and advice would be greatly appreciated.

Check your vehicles Tire Placard for the recommended tire inflation pressure.

Keep in mind that recommendation is based on a cold reading, before the tire is driven on and becomes hot, which will cause the air pressures to increase.
 
#13
Just use the factory recommended air pressures.

For passenger cars, (there are also truck XL tires, but that's a different scenario), the XL tires are for very high speed use of 100++ mph. When a tire is traveling at those very high speeds, the safe load carrying capacity is reduced and the tire can blowout. At those speed that will really ruin the day of the driver. So adding air pressure to maintain a safe load carrying capacity is needed, hence the need for XL tires that can safely withstand higher tire inflation pressures.

Also when a tire is traveling at very high speeds, its shape deforms a bit to more of an oblong shape than a circular one. This can actually cause the tire to come off of the wheel and again, at that speed the results wouldn't be very...positive, shall we say. Higher air pressures can help to reduce that tire deformation.

The drawback to XL tires is that they tend to ride very hard compared to the standard, "P", rated tires.

-- B.F.Goodrich T/A Certified Tire Specialist
 
#14
Ok so it won't cause the tire to separate from the rims or damage them or the tires in any way? I've done audio and video and mechanic work detailing and everything but never messed with tires and rims enough to know anything about them.
 
#15
No, using the normal air pressures listed for your car and tire combination is all that is needed for standard use, i.e. not traveling at very high speeds.

Check your owners manual for verification.

Have you located the tire placard for your car yet?
 
#17
The tire placard will not only list the recommended tire air pressures, but also the recommended size and load range of tire, (XL vs P, etc). This should match the tire that is on your car and so should the recommended tire air pressures.
 
#19
Start with 34 p.s.i. since you have less sidewall, and get a tire depth gauge. Every month, measure tread depth from the outside and inside of the tire, and average that number. Then measure the middle of the tire, and compare those two numbers.

If the middle of the tire has more depth, add pressure. Less depth ... reduce pressure.

When you go aftermarket wheels and tires, you have to play it by ear. I've seen Z-rated tires require up to 6 more p.s.i. than what the sticker called for because they were very soft.
 
#20
You want the tread depth gauge, because if you wait until you visibly can see a difference in wear, it is usually too late to have an even wearing tire at that point.
 
#22
I bought the tires and rim used online for $250 I've never heard of the company who makes the tires until I bought them there Venezia Crusade HP there 225/40zr18 92wxl m+s extra load tires the rims are massiv 914 cyclone
 
#23
When you go aftermarket wheels and tires, you have to play it by ear. I've seen Z-rated tires require up to 6 more p.s.i. than what the sticker called for because they were very soft.
Aftermarket wheels aren't the issue (although changing the stock tire size doesn't help), but even with stock rims and OEM tire size, harder or softer compound tires might require different air pressure than recommended on the placard.
 
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